The present disclosure generally relates to a method for humanely stunning and slaughtering poultry, and more particularly to a method for decreasing the spastic wing activity of poultry during slaughter. In particular, the birds are placed into a sealed chamber and the pressure in the chamber is reduced at a continuous rate to a target decompression pressure. Once the target decompression pressure is established, the rate of pressure reduction is gradually decreased for a period of time until the poultry achieves a state of death. The low atmospheric pressure slaughter disclosed herein is more humane than traditional slaughter techniques and results in less spastic wing activity.
In the poultry-processing industry, poultry, such as hens, chickens, turkeys and the like, is processed in slaughterhouses into products intended for human consumption. Before the birds can be processed, they must first be stunned and then killed. The stunning of the birds may be achieved, for example, by exposing the birds briefly to an electric voltage or by placing the poultry in a room containing a stun gas. The stunning, either by means of an electric voltage or in some other manner, renders the birds unconscious or semi-conscious, so that the birds will not struggle to free themselves during further processing and will not be conscious at the time of death. Once stunned, the poultry is typically slaughtered by cutting the neck, so that the poultry will bleed to death. Alternately, the poultry may be re-exposed to an electric voltage, and electrocuted.
At present, most birds are stunned by electrical shock. This method is generally reliable and safe. However, prior to stunning, the birds' legs are placed in shackles forcing them to remain in an upside-down position as they are stunned. This position raises the blood corticosterone, a hormone integral to the general well being of birds, indicating increased stress levels. Furthermore, the birds may struggle prior to being shocked, which can result in broken wings and other damage to the poultry, thereby reducing the value of meat obtained from the poultry, and also increasing the extent of suffering of the birds.
Gas stunning typically involves the introduction of gasses such as carbon dioxide plus other gases, including argon, nitrogen, and oxygen into a closed chamber. However, use of these gases may be dangerous to humans, can require excessively long exposure times, and often results in grand mal seizures in the birds, suggestive of extreme pain. In addition, in the event of plant shutdown during the gas stunning process, the birds in the chamber cannot be removed until the gases are safely exhausted, and any birds that are not yet dead may revive and will suffer greater stress.
Attempts have also been made to stun or slaughter animals using changes in pressure. For example, U.S. Pat. No. 4,829,635 to Tonnies discloses a method for stunning animals such as pigs before slaughter. The animal is enclosed in a chamber that is first evacuated to an intermediate pressure that is well below atmospheric pressure, until the animal loses consciousness but not reflexes. The chamber is then evacuated again to a low pressure well below the intermediate pressure, and the low pressure is maintained until the animal is without reflexes, but heart function remains.
U.S. Pat. No. 2,588,770 to Sadler discloses an apparatus and method for stunning or killing animals. The process involves a two step pressure drop, first to a pressure low enough to cause sleepiness or unconsciousness, and then to a lower air pressure which is sufficient to kill.
However, none of the methods used in the prior art take into consideration the effects of particular pressure levels and the time of pressure decrease on the humanity of the stun/slaughter process, and physiological behavior of the poultry, such as spastic wing activity, or the effects of these variables on meat quality. There is thus a need for a more humane method of stunning and slaughtering animals, and in particular poultry, that also results in less broken wings, and thus, an improved meat quality.